This invention relates to an automatic hammer for driving elongated members into the earth and for extracting such members from the earth.
Earth probing for environmental and geotechnical soil sampling has become increasingly necessary. Samples may be taken by drilling into the earth and taking samples at predetermined depths, or by driving samplers into the earth. Where possible, driving samplers directly is usually less expensive and more convenient than drilling. Samplers, rod, casing or other members are hammered into the earth by automatic hammers that apply impact forces to the member in a downwardly acting motion. However, samplers and other members driven into the earth in this way must usually also be removed. Existing automatic hammers are not capable of driving a sampler in both a downward direction and an upward direction. Several devices such as hoists, hydraulic cylinders, etc., are used to apply a steady, upward force to remove an object from the earth. However, impact force is more effective than a steady force in removing stuck objects from the earth.
One prior art method of driving samplers, rod, casing or other members into the ground employs a cathead (or power rotating drum) and rope to raise and drop a hammer. An operator engages the rope which is connected to the drop weight with the rotating drum. The drum raises the drop weight to a predetermined height, at which time the operator releases the rope to allow the drop weight to drop and thus impact the object being driven into the ground. Catheads may also be used to provide an upwardly directed impact force to drive members out of the ground. Catheads are dangerous to operate and must be used by skilled operators only. Their use has largely been replaced by the automatic hammer to drive members into the ground, which is a safer, more accurate method of driving rods, samplers, casing or other members into the ground. But since these automatic hammers are not capable of back driving, many rigs are still equipped with catheads for back driving.